In recent years, as land transportation vehicles, such as railway vehicles, automobiles, motorcycles and the like, become faster and larger, disc brakes become used more commonly as braking devices for those vehicles. A disc brake is a device that produces a braking force by means of friction generated by sliding contact between a brake disc and a brake lining.
As a disk brake for a railway vehicle, a donut-shaped brake disc is mounted and fastened to a wheel or an axle. A brake caliper presses a brake lining against a sliding surface of the brake disc, and thereby, a braking force is produced. In this manner, the rotation of the wheel or the axle is controlled, so that the running vehicle slows down.
During operation of the disk brake, noise that is called “brake squeak” occurs. Brake squeak is considered to occur based on the following principles. When the brake lining is pressed against the brake disk for braking, the friction between the brake lining and the brake disk causes the whole brake unit to vibrate unstably, that is, causes a “self-excited vibration” of the whole brake unit. The self-excited vibration is a vibration with its amplitude increasing. External steady energy turns into vibration energy inside the system, and the vibration energy vibrates the system itself. In this way, a self-excited vibration occurs. In order to suppress the brake squeak, it is necessary to suppress the self-excited vibration caused by the friction during the braking motion.
Japanese Patent Application Publication No. 2002-340056 (Patent Literature 1) discloses a disk brake wherein a piston presses a pad against a brake disk. In the disk brake, the pad is moved downstream along the rotation of the brake disk and moved toward a trailing side (contact ending side) by the frictional resistance of the pad pressed against the brake disk. Accordingly, the contact area of the piston with the pad is greater in the trailing side that is downstream with respect to the rotation direction of the brake disk than in the leading side that is upstream with respect to the rotation direction of the brake disk. Patent Literature 1 states that this structure suppresses self-excited vibration and thereby suppresses brake squeak.
Japanese Patent Application Publication No. 2011-214629 (Patent Literature 2) discloses a brake lining including a base plate and a plurality of friction members. Each of the friction members is fastened to the base plate via an elastic member. The support stiffness of the elastic member depends on the position of the friction member on the base plate. Patent Literature 2 states that this structure suppresses brake squeak.
Japanese Patent Application Publication No. 2012-251597 (Patent Literature 3) discloses a brake lining including a base plate and a plurality of friction members. FIG. 1 is a plan view showing the structure of the brake lining disclosed in Patent Literature 3. In the brake lining 32, each of the friction members 33 is fastened to the base plate 36 via an elastic member. Each of the friction members 33 is supported by the base plate 36 with a portion including the center fastened to the base plate 36. Two adjacent friction members 33 are connected by a back board 34. The friction members 33 are circular in planar shape, and the friction members 33 are substantially equal in diameter.
The back board 34 includes circular disk portions which are almost the same size and shape as the friction members 33 in a planar view, and a connection portion connecting these two circular disk portions. The width (dimension in a direction perpendicular to the length direction of the back board 34) of the connection portion is smaller than the widths of the circular disk portions. Accordingly, the back board 34 as a whole is narrow in the middle with respect to the length direction.